The Upanishads are one of the main philosophical texts of Hinduism. Many of these works were composed in Sanskrit between around 800-400 B.C.; newer Upanishads were composed in Medieval times. New discoveries of lost works are still being discovered. As a result there are more than two hundred recognised Upanishads. The works discuss the importance of Brahman and Atman: the Universal Spirit and the Individual Self, and the relationship between these two concepts.

It is possible that, as Indian religious scholars visited Ancient Greece, the Upanishads could have influenced early Greek thought. Parallels between Plato's philosophy and concepts in the Upanishads can be easily discovered.